On Mon, August 2, 2010 14:50, Adrian Walker said:
>
> Rich, you wrote... *negation as failure is more human like*... (01)
I dispute Rich here. If a human believes that the complete extent of
some relation is known (if some of the variables are fixed), then they
use negation as failure, because that is implicit in the complete extent
being known. If a human does not believe the complete extent of the
relation is known then s/he is unlikely to reason with negation as
failure." (02)
> Indeed, relational databases, on which much of the world economy runs, use
> a form of negation-as-failure -- If Adrian is not in the table of
> employees of Englishlogickernel, then he is not an employee
> of said company. (03)
> Just commonsense, really. (04)
This "commonsense" relies on an understanding of the definition of the
table. If this definition is encoded in logic, then the NAF reasoning
appears in an open world environment. (05)
Such database tables are even more restrictive than NAF. They rely on
"negation-if-not-asserted". They don't allow reasoning to conclude that a
person is an employee. If lookup fails, they aren't. (06)
What is given for this table is that all values of ?EMP are asserted for
hasEmployees(Englishlogickernel, ?EMP) (07)
Negation-if-not-asserted is valid for the second argument of this predicate
when the first argument has a specific value. It is not valid if the
first argument has a different value, nor is it valid if the second
argument is specified, and not the first. E.g., suppose we are given
hasEmployees(Englishlogickernel, JohnDoeEsq)
Common sense won't tell us whether or not there is another company such
that
hasEmployees(?COMPANY2, JohnDoeEsq) AND
NotEqual(Englishlogickernel, ?COMPANY2)
NAF should not be used when answering such a request. (08)
Cyc uses the rule macro predicate completeExtentAssertedForValueInArg to
specify such relations. If this is asserted for a predicate, the
reasoning engine can answer FALSE for a matching query if no matching
statement is asserted. (09)
E.g., given
(completeExtentAssertedForValueInArg hasEmployees Englishlogickernel 1)
in some context, Cyc will answer FALSE to the query
(hasEmployees Englishlogickernel Adrian)
in the same context (or a subcontext) if the queried statement is not
asserted. (010)
To allow NAF (i.e., after reasoning) Cyc uses the more general relation,
completeExtentDecidableForValueInArg. (011)
-- doug foxvog (012)
> Moreover, if you attach English sentences to predicates [1], you can help
> nontechnical users to know what's going on by answering the question
>
> "Is Adrian an employee of Englishlogickernel?"
>
> with
>
> "Assuming that the table lists all the employees, he is not an employee of
> that company"
>
> Cheers, -- Adrian
>
> [1] Internet Business Logic
> A Wiki and SOA Endpoint for Executable Open Vocabulary English Q/A over
> SQL and RDF
> Online at www.reengineeringllc.com
> Shared use is free, and there are no advertisements
>
> Adrian Walker
> Reengineering
>
>
>
>
> On Mon, Aug 2, 2010 at 1:54 PM, Rich Cooper
> <rich@xxxxxxxxxxxxxxxxxxxxxx>wrote:
>
>> Hi Ian,
>>
>> If the intent of the tool's designers is to mimic human perspectives on
>> knowledge and logic, then negation as failure is more human like, IMHO,
>> than
>> any existing alternative. A person with no experience in an area
>> normally
>> is very skeptical of assertions that can't be proven within his/her
>> database
>> of factual and structural knowledge, and reaches the same conclusion.
>> I'm
>> sure you've heard it said that you don't know what you don't know, so
>> you
>> assume you know everything until proven otherwise.
>>
>> Another way to look at it is that, within the bounds of evidence, a
>> judge
>> or
>> juror has no basis for any conclusion that is not consistent with known,
>> demonstrated facts. It is always possible that other information will
>> surface in the future, but the rational deduction of the present moment
>> has
>> to be based on known facts, not on missing information.
>>
>> One consequence of this result is that it is very hard to convince
>> anyone
>> of
>> a fact which has no familiarity, in specific or general terms, to them
>> personally. That is why attorneys and laws depend on known facts.
>>
>> -Rich
>>
>> Sincerely,
>> Rich Cooper
>> EnglishLogicKernel.com
>> Rich AT EnglishLogicKernel DOT com
>> 9 4 9 \ 5 2 5 - 5 7 1 2
>>
>> -----Original Message-----
>> From: ontolog-forum-bounces@xxxxxxxxxxxxxxxx
>> [mailto:ontolog-forum-bounces@xxxxxxxxxxxxxxxx] On Behalf Of Ian
>> Horrocks
>> Sent: Monday, August 02, 2010 10:14 AM
>> To: edbark@xxxxxxxx; [ontolog-forum]
>> Cc: Bernardo Cuenca Grau
>> Subject: Re: [ontolog-forum] owl2 and cycL/cycML
>>
>> It is even more tricky that this. The failure in "negation as failure"
>> doesn't mean failure of a given algorithm, it means not provably true.
>> There
>> are many decidable logics with NAF. If we have an incomplete reasoner
>> for
>> such a logic, we are *still* incorrect if we take failure to return
>> "True"
>> as being equivalent to "False", because the failure may simply be a
>> symptom
>> of the incompleteness and nothing to do with NAF.
>>
>> Simple example: I am using a logic in which negation is interpreted as
>> NAF.
>> I have a simple boolean theory in which negation isn't used and which
>> entails A(x). I ask if A(x) is entailed. My incomplete (for entailment)
>> reasoner answers "False". If I treat this as entailing that A(x) is not
>> entailed, then I am really incorrect -- nothing to do with NAF.
>>
>> In fact I think that we would be well advised to strike NAF from the
>> record
>> -- it's really not helpful in this discussion :-)
>>
>> Ian
>>
>>
>>
>>
>>
>> On 2 Aug 2010, at 17:45, Ed Barkmeyer wrote:
>>
>> >
>> > Ian Horrocks wrote:
>> >
>> >> Regarding my claim that reasoners are typically used in a way that is
>> actually incorrect, to the best of my knowledge none of the incomplete
>> reasoners in widespread use in the ontology world even distinguish
>> "false"
>> from "don't know" -- whatever question you ask, they will return an
>> answer.
>> Thus, in order to be correct, applications would have to treat *every*
>> "false" answer as "don't know". I don't know of any application that
>> does
>> that.
>> >>
>> >
>> > Put another way, it is not incorrect to treat "don't know" as "false",
>> > if "negation as failure" is a stated principle of the reasoning
>> > algorithm. We can state the 'negation as failure' principle generally
>> > as "if the assertion cannot be proved from the knowledge base, the
>> > assertion is taken to be false."
>> >
>> > Of course, "proved" means that the reasoning algorithm can derive a
>> > proof, which depends on the algorithm actually implemented in the
>> > engine. As Ian mentioned earlier, this kind of "proof" implies that
>> the
>> > nature of the reasoning algorithm is, or incorporates, "model
>> > construction", which is typical of various kinds of logic programming
>> > engines, but there are many hybrid algorithms.
>> >
>> > -Ed
>> >
>> > --
>> > Edward J. Barkmeyer Email: edbark@xxxxxxxx
>> > National Institute of Standards & Technology
>> > Manufacturing Systems Integration Division
>> > 100 Bureau Drive, Stop 8263 Tel: +1 301-975-3528
begin_of_the_skype_highlighting +1
301-975-3528 end_of_the_skype_highlighting
>> > Gaithersburg, MD 20899-8263 FAX: +1 301-975-4694
>> >
>> > "The opinions expressed above do not reflect consensus of NIST,
>> > and have not been reviewed by any Government authority."
>> >
>> >
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=============================================================
doug foxvog doug@xxxxxxxxxx http://ProgressiveAustin.org (014)
"I speak as an American to the leaders of my own nation. The great
initiative in this war is ours. The initiative to stop it must be ours."
- Dr. Martin Luther King Jr.
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